Field of the Invention
The invention relates to energy supply systems, energy management units, and methods for supplying local and regional energy systems and energy consumers with power according to the preamble of the independent claims.
Discussion of Related Art
Known energy supply systems are based on the concept that centralized energy-generating units make energy available in a certain form, for example as electrical energy, as thermal energy in the form of hot water or hot steam (district heating), or as chemical energy in the form of natural gas, and deliver these via suitable power systems to a multitude of energy consumer units.
When supplying energy to a plurality of spatially distributed energy consumer units, for example households with electrical power, the sufficient dimensioning and structuring of the corresponding supply network is a fundamental factor for ensuring sufficient supply power and security of supply.
Supply networks often comprise various hierarchy levels. Several local or regional consumer units can be grouped together into a local network which, in turn, can be connected to a higher-level network. In the case of a power network, for example, a plurality of small consumer units, different households, for example are connected to a common, local low-voltage grid. Different low-voltage networks, in turn, are connected via transformers to a medium-voltage network that is used for regional energy transport. A high-voltage distribution network is used to transport the electrical energy from large power stations over long distances to the medium-voltage networks. Smaller power stations can also feed the energy into the medium-voltage network, and local energy producers, such as photovoltaic systems or wind power stations, for example, into the low-voltage network.
Another example of a supply network is a district heating system, in which heat energy is produced in the form of water vapor or hot water (for example, 120° C., 16 bar) and transported via a primary circuit to the various consumer units, where it is used to heat buildings and produce hot water. In common district heating systems, the heat energy is produced centrally in a combined heat and power plant, for example in a woodchip heating system or a waste-incineration plant. The energy consumers are connected via suitable heat exchangers directly, or indirectly via a local secondary circuit, to the primary circuit of the district heating system. Analogously to district heating networks, district cooling networks also exist, although it is basically heat energy that is transported in those as well.
In the case of energy supply via a spatially distributed supply network that is fed by one or more energy producers, the required capacity both of the supply network and of the energy producers results from the maximum required peak energy requirement of the energy consumers. This energy requirement is generally subject to substantial time fluctuations. In a district heating network, for example, consumption peaks occur in the early morning and in the late evening, whereas in an electrical grid, consumption peaks occur in the morning, at midday and in the evening.
As a result of the fluctuating energy demand, a spatially distributed supply network must be designed for a multiple of the average energy throughput. In district heating systems, for example, the lines must be designed such that they can handle the expected maximum daily consumption peak on the coldest day of winter. A supply network with an excessively weak design can lead to insufficient energy supply as a result of a capacity bottleneck.
In the case of a power network, overloading can even lead to a collapse of the grid. The fuses disposed at the nodes of the network having an upper limit of 1000 A, for example, are crucial in this regard. In a network designed for 50 kV, this results in a maximum output of 50 MW, and in a network designed for 25 kV, in a maximum output of 25 MW. Since the investment costs for supply networks rise disproportionately to their capacity due to more expensive technology, lower consumption peaks can result in substantial savings in the construction and operation of the network.
Analogously to the supply network, the energy producers must also be capable of covering the consumption peaks. In the case of electrical power stations, slow power stations for the base load production (nuclear power stations, coal-fired power plants, run-of-the-river hydro power stations, wind power stations, etc.) and quick-starting power stations for the peak load production (storage hydro power stations, gas-fired power plants, etc.) are combined for this purpose. The necessary excess capacities also result in higher investment costs.
Due to the growing number of small power stations connected to regional or local power networks, such as photovoltaic systems and wind power stations, for example, the fluctuations in production turn out to be difficult to forecast for the network operator. What is more, since the network operators are in part obligated for legal reasons to feed the locally produced energy into the network, production cannot even be controlled in some cases. These additional energy production peaks must also be taken into account during the designing of the networks and further reduce the average usable capacity.
Various approaches are known for achieving a more uniform loading of energy supply networks, and thus for achieving a lower required capacity of network and energy producers, as well as improved energy efficiency as a result of the associated lower losses.
For the power supply, so-called smart grids are used in the attempt to achieve a spatially and temporally maximally homogeneous loading of the network through coordination of different flexible and non-flexible energy production systems, energy storage systems (pumped storage power plants) and energy consumption systems. For this purpose, the various components of the smart grid communicate with one another. This has its limits, in that the local consumption and local production of electrical energy can be controlled from the outside only to a limited extent.
In district heating systems, through the use of appropriate heat energy stores in the form of hot-water tanks or latent heat accumulators (as shown in DE 2730406 C2, for instance), fluctuations in the energy demand over the course of the day can be evened out. It is known, for example from DE 2730406 C2, to balance out the energy requirement over a day through the use of suitable heat accumulators, for example hot-water tanks or latent heat accumulators. Through the appropriate coupling of hot water accumulators, heating systems and hot water preparation, the efficiency of the heat utilization can be improved, for example as described in DE 10311091 B4 and DE 3123875 C2.
In the article “Technology Planning for Electric Power Supply in Critical Events Considering a Bulk Grid, Backup Power Plants, and Micro Grids,” IEEE Systems Journal 4(2), p. 167, Jun. 3, 2010, A. Kwasinski discusses the risk assessment of energy supply systems in natural disasters using the example of three technological options for supplying local networks with power, namely connection to an external network by means of a substation; a backup diesel power station at the interface between local network and external network; and a microgrid with its own energy production, for example power generators driven by gas turbines.
In their article “Cutting Campus Energy Costs with Hierarchical Control,” IEEE Electrification Magazine September 2013, p. 40, Sep. 23, 2013, M. Shahidehpour et al. describe a microgrid at the Illinois Institute of Technology in which power generators are operated by means of gas turbines in order to balance out power outages on the external supply network. Accumulators are used to bridge over short-term power outages without the use of generators. Other aspects are controlling the system in view of the costs of the energy obtained, the construction of the internal power network with several separate supply circuits in order to reduce internal power outages to a minimum in buildings, and the integration of renewable energy sources (photovoltaics, wind energy) into the local network.
There is a general need for optimally efficient energy supply networks that also preferably involve minimal new investments.